Swirl Perlin Noise Generator

Question

I have this code to generate 1D noise in obj-c, it works fine:

- (float)makeNoise1D:(int)x { x = (x >> 13) ^ x; x = (x * (x * x * (int)_seed + 19990303) + 1376312589) & RAND_MAX; return ( 1.0 - ( (x * (x * x * 15731 + 789221) + 1376312589) & RAND_MAX) / 1073741824.0); } 

Now I'm trying to play it in Swift, but it always fails and shows EXEC_BAD_INSTRUCTION on return. Here is what it looks like now, I had to spit out the final expression, but I'm sure that is not a problem.

 func makeNoise1D(var x : Int) -> Float{ x = (x >> 13) ^ x; x = (x * (x * x * seed! + 19990303) + 1376312589) & 0x7fffffff var inner = (x * (x * x * 15731 + 789221) + 1376312589) & 0x7fffffff return ( 1.0 - ( Float(inner) ) / 1073741824.0) } 

I have already tried many different butts and divided into subexpressions, but still fails. The only thing I realized was that the first and last line worked. (Most of my test cases x were set to 20, and the seed to 10, just to make it simple).

Thanks for the help!

Answer 1

The exception is caused by an "arithmetic overflow" that occurs if the result of one of your calculations cannot be represented as Int .

Unlike (Objective-) C, adding and multiplying integers in Swift does not “wrap” or “truncate,” but it causes an error if the result does not fit into the data type.

But instead, you can use Swift "overflow operators" &* and &+ , which always truncate the result:

 func makeNoise1D(x : Int) -> Float{ var x = x x = (x >> 13) ^ x; x = (x &* (x &* x &* seed! &+ 19990303) &+ 1376312589) & 0x7fffffff let inner = (x &* (x &* x &* 15731 &+ 789221) &+ 1376312589) & 0x7fffffff return ( 1.0 - ( Float(inner) ) / 1073741824.0) }